Before Darwin developed the theory of natural selection and MIT's Alan Guth developed that of the inflationary universe, most scientists ignored or accepted as givens certain observations that couldn't be explained by the existing theories of creationism and the big bang. After Darwin and Guth advanced their ideas, however, these same observations were recognized as anomalies in the previous theories.
Such "retro-recognition" of certain scientific anomalies has happened again and again over the history of science, argue Alan Lightman of MIT and Owen Gingerich of the Harvard-Smithsonian Center for Astrophysics in the February 7 issue of Science. The phenomenon, they say, reveals important features of the process of scientific discovery and of human psychology.
In the Science article Dr. Lightman, a professor of science and writing, senior lecturer in physics, and head of the MIT Program in Writing and Humanistic Studies, and Dr. Gingerich give five examples of the retro-recognition phenomenon that cut across the disciplines of cosmology, geology, biology and physics. The first, which they call "The Flatness Problem," concerns an anomaly of the big bang theory that most cosmologists accepted only after Professor Guth, now Jerrold Zacharias Professor of Physics, came out with his model of the inflationary universe.
According to the big bang theory the universe has been expanding ever since the explosion it was born in. However, the authors write, "competition between the outward motion of expansion and the inward pull of gravity leads to three possibilities [about the future of the universe]." The universe may expand forever, halt and reverse the expansion, or reach some "flat" point between the two.
To infer what will happen scientists are comparing the universe's present gravitational energy with its present kinetic energy of expansion. If the first of these energies is greater, the authors say, the universe will reverse its expansion and "is fated to collapse at some time in the future"; if the second is greater, it will continue to expand; and if both are equal, the universe is flat.
To date, scientists have found that the two energies are very nearly balanced, indicating that the universe is almost flat. But such a situation would require that the gravitational energy and kinetic energy of expansion were almost perfectly balanced at the beginning of the universe, too-a scenario that seems unlikely.
But few scientists questioned this assumption, or saw it as an anomaly. Rather, they regarded such a close initial balance of the energies "as a given or accidental property of our universe and saw no difficulty with the near flatness of the cosmos," the authors write.
Then in 1981 Professor Guth proposed his theory of the inflationary universe. According to that, the authors write, "the matter and energy in the infant universe existed in a peculiar state, behaving as if they had repulsive gravity and resulting in a very brief period of extremely rapid cosmic expansion." One of the consequences of this inflationary expansion is that the gravitational energy and kinetic energy of expansion would be driven to very similar values. So Professor Guth's theory explains in a natural way the close balance scientists have observed.
Professors Lightman and Gingerich point out that the inflationary universe model "is by no means universally accepted among practicing cosmologists, nor is the legitimacy of the flatness problem." However, they say, since the model was proposed "many more cosmologists recognize the peculiarity of the observational facts."
As a further example of the retro-recognition phenomenon, the authors related "The Continental-Fit Problem." Since the early 17th century, Professors Lightman and Gingerich write, scientists have been aware of the "remarkable similarity of shapes of the opposite coasts on the two sides of the Atlantic. South America and Africa, in particular, are shaped as if they were two fitting pieces of a jigsaw puzzle."
But because geologists believed that land masses on Earth could move only vertically, they assumed that the similarities were "accidental." Though a few scientists suggested that the two continents were once joined, they weren't taken seriously. Even Alfred Wegener's theory of continental drift, which was supported by geological and fossil evidence, remained controversial until the mid 1960s. Wegener had proposed the theory in 1912.
Then in the late 1960s came the theory of plate tectonics. "This theory, for the first time, provided a persuasive mechanism by which the continents could move horizontally-namely, the existence of a series of `plates' on which the continents sit," the authors write.
In summary, they say, "What was for Wegener a clear anomaly in need of a reasoned explanation had been for the great majority of geologists just a curiosity. . . Only after the paradigm changed was the fit of the continents seen as an anomaly pointing the way to a major new way of looking at the stability of continental arrangements."
Professors Lightman and Gingerich suggest in the Science article that the retro-recognition phenomenon can be explained by both the nature of science itself and human psychology.
For one, they say, science is a conservative activity. Such conservatism "has the short-term asset of allowing each current conceptual framework to be articulated so clearly that it . . . can serve as an organizing principle for the multitude of acts that scientists observe," but it can sometimes prevent the adequate recognition of observations that don't fit within the current theory. In addition, scientists may be reluctant to accept new theories (or recognize anomalies in the old) "for the purely psychological reasons that the familiar is often more comfortable than the unfamiliar, and that inconsistencies in belief are uncomfortable."
In conclusion, the authors write, "If unexplained facts can be glossed over or reduced in importance or simply accepted as givens, the possible inadequacy of the current theory does not have to be confronted. Then, when a new theory gives a compelling explanation of the previously unexplained facts, it is `safe' to recognize them for what they are."
A version of this
article appeared in the
February 12, 1992
issue of MIT Tech Talk (Volume